Volleyball Material:
There are many varying types of volleyballs for indoor and outdoor usage. The indoor balls tend to have a lighter material that is used to gym wear and tear. The outdoor balls have waterproof materials that are resistant to the friction of the sand.

Indoor Volleyballs:
-Leather
-Synthetic Leather, better to withstand the beating on a gym floor
-Most balls are filled with Butyl

Outdoor Volleyballs:
-Neoprene, a material similar to that of wetsuits
-Rubber, an all weather material
-Butyl Bladder, the balls are filled with this gas to give it "true bounce and flight" (mikasasports.com)